Electric rheostat.



110,841,232. PATENTED JAN. 15, 1907. W. F. DANA & H. W. KNQTT.

ELECTRIC RHEOSTAT. APPLICATION FILED JULY 26', 1905.

WITNESSES: down and bind in the buttons.

UNITED STATES PATENT OFFICE.

WILLIAM DANA AND HENDERSON W. KNOTT, OF NEW YORK, N. Y.

ELECTRIC RHEOSTAT.

Specification of Letters Patent.

Patented Jan. 15, 1907.

Application filed July 26,1905. Serial No- 271388.

To all whom it may concern.-

Be it known that we, WILLIAM F. DA A, a citizen of the UnitedStates,'and HENDERSON W. KNOTT, a subject of the King of Great Britainand Ireland, residing at New York city, in the county of New York andState of New York, have invented a new and useful Improvement inElectric Rheostats, of which the following is a specification.

' Our invention relates to rheostats in which the electric current isgradually increased from a desired minimum to a desired maximum by themeans of a series of graduated resistances. In such rheostats now in usethe contact between the switch and the several resistances is usuallyeffected by intervening wires duly attached and insulated, and therheostat becomes in consequence cumbrous and complicated. The object ofour improvement is to construct a rheostat which shall be simple andcompact in form.

Our method is to provide strips or buttons of gradually-increasingdegrees of resistance and to arrange them consecutively in 00-.

lumnar form with an alternating series of metallic contact-plates. Theseresistances are composed of graphite and clay (preferably Germanclaylpowdered and mixed to gether, pressed into the form of buttons ofsimilar design and shape, and baked. The graphite and clay when thusbaked is brittle and inclined to crack and break off in case therheostat sustains a jar or shock. It is therefore essential that thebuttons be partially inclosed. This is effected by either bending theprojecting edges of the metallic contact-plates over against theresistancebuttons, or preferably by causing their surfaces to behollowed out or recessed, so that thecontact-plates assume a cup-likeshape and are thus adapted to receive, surround,

Because of the brittle character of the baked graphite and clay and ofits naturally irregular cleavage it is practically impossible to effecta complete and erfect. contact between the surfaces *of the uttons andthe surfaces of the metal plates without some intervening medium. 0overcome this difficulty, we introduce between them a graphitic aste,whose conductivity is similar to t at of the metal plates, and with itwe securely cement those surfaces together in close and uniform contact.The method above describedpermits the arrangement of separateresistances in a simple, secure, and compact form, such as is notpossible in rheostats where connections are made by wire, and it therebydispenses with the use of wire and with the expense of wiring betweenthe resistances and contactpieces.

Our invention is illustrated in the accompanying drawings, in whichFigure 1 is a front view of our improvement complete and ready to beinserted in a rheostat-frame. Fig. 2 is a detailed sectional view of'thesame, showing the method of connecting the resistance-buttons to thecontact-plates, in form of a column and of insulating them from theircommon support. Figs. 3 and 4 illustrate one of said plates and one ofsaid resistance-buttons, res ectively.

Similar letters refer to simi ar parts throughout the several views.

The buttons A are composed of graphite and clay, as above described.They are similar in design and form and are of different and graduateddegrees of resistance, the degree of resistance being'in inverseproportion to the amount of graphite present in the mixture. The'buttonsA are consecutively arranged upon and in alternation with thecontact-plates B. These plates are made of metal and project beyond theedges of the buttons A. They are similar in form and are preferablyflattened at one edge I). The surfaces of the plates B are hollowed outor recessed, so as to receive the buttons A, which fit in them closely.These recesses are of sufficient depth to bind the buttons in and toprevent them from breaking or crumbling in case the rheostat suffers aviolent shock or jar.

As above set forth, it is practically impossible without a medium toeffect a perfect contact between the surfaces of the buttons and therecessed surfaces of the contact- Elates. To fill up the interstices andspaces etween the adjacent surfaces and to cement them together, we haveprovided a paste of high conductivity. This paste is composed ofpowdered graphite, pure carbon-dust, and gum-tragicum mixedtogether inthe propor tions of six, three, and one, ,respectively. Sufficient wateris added to secure to the mixture the proper consistency of paste. Inpreparing the above composition the aphite must be first freedfromallgaseous e ements by subjecting it to intense heat.

The buttons A and the plates B are placed one upon the other andcemented to ether in the form of a column and are secure in position bya bolt C passing through them alland fastened into the frame of therheostat. The bolt C is furnished at its ends With the nuts M and M. Thebuttons A and the contactlates B are insulated from thebolt C and f r omits said nuts by the'insulating mate rial D. The flattened edges bof thecontactplates B are arranged in the sameplane; and thusv present an evencontact-surface, -over and upon which any -contact-switch with Whichrheostats are commonly furnished may-be swept or mani ulated, thusbringing the (lifferentandrgra uated resistance-buttons consecutivelyinto circuit.

We are aware that-ineither a-lseries of resistances with interposed:metallici contacts .nor aswitchadaptedtowbe manipulated in the patlrofsuch contectsarenew in themselves, and We .make. no claimhereinafterbroad enough to include such-series or such switch.

What We claim as our inventionpand desire tosecure :by LettersPatent;is-

, 1. A rheostat comprising a series of resistances composedofggraphiteand clay, alternating with interposed metallic contactplates,the surfaces ofl-which-are sufficiently recessed to closely-receiveandrigidly hold said resistances in su erficial contact, and to protectthem from s oek -ori-other external injury,- substantially as described.1

2. A rheostat Whose resistances are composed of graphite and clay mixedand formed into buttons ofsimilar form, and cemented in closesuperficial contact to interposing metallic contact-plates by agraphitic paste of high conductivity, substantially as described.

3. The combination, in a rheostat, of graphiteand clayresistance-buttons and of interposed metallic contact plates,alternating therewith and collrrifpletely united thereto at theirrespective su aces byz a graphitic paste,

" composed ofzpowderedgraphite pure carbondust -gum-tragicume and watermixed: together, substantially asdescribed.

A. Airheostat com rising the'resistancebuttons A, similar; in crmandofrgraduated degreesiof resistance, rigidly'heldin alternate ing serieswith and protected by the recessed contact-plates Bzand united to themdncomplete contactat their-respective surfacesby a graphitic .=paste ofhigh conductivity,-= all arranged 'inform of" a column.- andso adaptedthat a contact-swzitch may be-mani-pulatediin the path of saidcontact-plates; substantially names to this specification in thepresenceof two subscribing-witnesses.

JOHN-M. NOLAN,

WALTER H. Donn.

